I can confirm the issue (also using BT747). Actually, I thought that the better approach would be to package 2.2pre2 instead of 2.2pre1; this is also the version natively used by BT747.
The main problem with not being able to use Fedora's rxtx is that the version bundled with BT747 tries to get its lock in /var/lock (aka /run/lock, only writable by root) instead of /var/lock/lockdev (writable by group lock).